Vanadium-51 NMR Research Articles

Activating tert-butyl hydroperoxide by chelated vanadates for stereoselectively preparing sidechain-functionalized tetrahydrofurans

tert-Butyl hydroperoxide (TBHP) stereoselectively oxidizes substituted 4-pentenols, when activated by (ethyl)[cis-(piperidine-2,6-diyl)dimethyl] vanadates. The reaction affords (tetrahydrofuran-2-yl)methanols in up to 89% yield, and in stereoselectivity ranging between moderate (cis:trans=32:68) to excellent (>99:1). Correlating structures of 4-pentenols, differing by substitution at tetragonal and trigonal stereocenters, to configuration of products obtained from oxidative cyclization provides a reaction model explaining the origin of stereoselectivity by (i) intramolecular oxygen atom transfer to (ii) a chair-like folded alkenol, being (iii) hydrogen-bonded to one of the two aminodiolate oxygens of the chelated vanadate, having (iv) substituents in the chair-like transition structure preferentially aligned equatorially. Substituents at trigonal stereocenters improve 2,5-cis- and 2,4-trans-selectivity for oxidative 4-pentenol cyclization in case of (Z)-configuration. An (E)-substituent does not alter selectivity exerted by a terminal (Z)-substituent of similar steric size. Larger (E)-groups increase the fraction of 2,5-trans-cyclized products. The reaction model additionally implements results from vanadium-51 NMR spectroscopy and density functional theory. According to theory, the (dialkoxy)(oxo)vanadium substituent exerts in the preferred end-on conformation almost no effect on structure and bonding of the peroxide group in tert-butylperoxy vanadates. Changing conformation to a higher in energy side-on arrangement puts the vanadate-bound tert-butylperoxy group into a position to serve in a concerted reaction as combined electron acceptor and oxygen atom donor.

Acidification of Reverse Micellar Nanodroplets by Atmospheric Pressure CO2

Water absorption of atmospheric carbon dioxide lowers the solution pH due to carbonic acid formation. Bulk water acidification by CO(2) is well documented, but significantly less is known about its effect on water in confined spaces. Considering its prominence as a greenhouse gas, the importance of aerosols in acid rain, and CO(2)-buffering in cellular systems, surprisingly little information exists about the absorption of CO(2) by nanosized water droplets. The fundamental interactions of CO(2) with water, particularly in nanosized structures, may influence a wide range of processes in our technological society. Here results from experiments investigating the uptake of gaseous CO(2) by water pools in reverse micelles are presented. Despite the small number of water molecules in each droplet, changes in vanadium probes within the water pools, measured using vanadium-51 NMR spectroscopy, indicate a significant drop in pH after CO(2) introduction. Collectively, the pH-dependent vanadium probes show CO(2) dissolves in the nanowater droplets, causing the reverse micelle acidity to increase.

Polyoxoanion with Octahedral Germanium(IV) Hetero Atom: Synthesis, Structure, Magnetism, EPR, Electrochemistry and XPS Studies on the Mixed-Valence 14-Vanadogermanate [GeVV 12VIV 2O40]8−

The mixed-valence 14-vanadogermanate [GeVV 12VIV 2O40]8− (1) has been synthesized and characterized in solution by 51V-NMR, UV–vis and electrochemistry and in the solid state by IR, magnetism, EPR, XPS and elemental analysis. Single-crystal X-ray analysis was carried out on K2Na6[GeVV 12VIV 2O40]·10H2O (KNa-1), which crystallizes in the orthorhombic system, space group Immm, with a=10.9623(3) A, b=11.6205(3) A, c=20.2658(5) A, and Z=2. Polyanion 1 is composed of a central GeIVO6 octahedron which is surrounded by a total of 14 VO6 octahedra. Vanadium-51 NMR in solution results in three peaks with intensity ratio of 8:4:2 which is in complete agreement with the solid state structure. The presence of two VIV centers was established by UV–vis, electrochemistry, magnetism, EPR, XPS and elemental analysis. Electrochemistry revealed that the two VIV-centers in 1 are oxidized through a single well-defined step, which does not split with changes in scan rate or pH. Polyanion 1 is also an active two-electron oxidation catalyst for the coenzyme NADH at pH 8, unprecedented in polyoxometalate chemistry. Magnetic susceptibility, magnetization and EPR data on KNa-1 complement the X-ray and electrochemistry results by confirming the presence of two unpaired electrons per molecule of 1. The two VIV ions possessing the spin are very weakly coupled, essentially acting as two well-isolated S=1/2 ions. The observed g-value of 1.977 from EPR and magnetic susceptibility measurements is consistent with literature reported value for a VIV ion, suggesting a possible ground state of $$3d_{x^{2}-y^{2}}.$$ XPS measurements on KNa-1 also confirmed the coexistence of VV and VIV in 1.

Solid-State Vanadium-51 NMR Studies of Supported V2O5−WO3/TiO2 Catalysts

Solid-state wide-line vanadium-51 NMR spectra of supported V2O5−WO3/TiO2 catalysts were obtained under ambient conditions. A distorted tetrahedral vanadium unit is favored at low vanadia loadings i...

Near UV circular dichroism from biomimetic model compounds define the coordination geometry of vanadate centers in MeVi- and MeADPVi-rabbit myosin subfragment 1 complexes in solution

The circular dichroism (CD) spectrum was measured from vanadate (Vi) cyclic esters of chiral vicinal diols, hydroxycarboxylates, and cyclodextrines as a function of Vi concentration ([Vi]) and at the lowest energy transitions of the vanadium. At low [Vi] and in the presence of excess vicinal diols, hydroxycarboxylates, or cyclodextrines the CD signal intensity scales linearly with [Vi] indicating the predominance of a monomeric cyclic ester. At higher [Vi], the signal intensity in the presence of the vicinal diols and hydroxycarboxylates become nonlinear in [Vi], indicating formation of a dimeric cyclic ester. Vanadium-51 NMR ( 51V-NMR) indicates the coordination geometry of several of these model Vi centers in solution and identifies the CD signals characteristic to Vi trigonal bipyramidal (tbp) and octahedral (Oh) coordination geometries from monomeric and dimeric species. The CD spectra from monomeric and dimeric forms of the tbp-coordinated model compounds have two apparent transitions with amplitudes of opposite sign at wavelengths≥240 nm. Spectra from the monomeric and dimeric Oh coordinated species are distinct from the tbp-type spectra over the same wavelength domain because of the presence of two additional transitions with opposite sign amplitudes. These model spectra were compared to the vanadate CD spectra from Vi bound to rabbit myosin subfragment 1 (S1) in solution, in the presence of divalent metal cations (MeVi-S1) or trapped with MeADP (MeADPVi-S1). Polymeric MeVi binds to the active site of S1 and the vanadate centers in MnVi-S1 or CoVi-S1 produce a CD signal resembling that from the tbp model. The trapped ATPase transition state analog MeADPVi produces a different CD signal resembling that from the Oh model.

Linear Chain Formation by an Oxovanadium(V) Complex of p-Methylhexahomotrioxacalix[3]arene.

The oxovanadium(V) complex 4 can be readily synthesized by the reaction of the lithium salt of p-methylhexahomotrioxacalix[3]arene trianion 3 with VOCl(3). Infrared spectra indicate a terminal V=O for complex 4 in solution and V=O.V dative interactions in the solid state consistent with the formation of a &mgr;-oxo-bridged linear chain polymer 1 (M = V, Y = O, X(3) = trianion of macrocycle 2a). Vanadium-51 NMR spectra indicate increased shielding for the linear chain polymer in the solid state compared to complex 4 in solution. Complex 4 and its linear chain polymer are proposed to have the oxovanadium group contained within the cup of the macrocycle ligand as shown in structures 5 and 7, respectively, where the cone represents macrocycle 2a.

Metal-ion binding properties of the transferrins: A vanadium-51 NMR study

Transferrins can bind a wide range of di- and trivalent metal ions. They have a bilobal structure where each domain contains a deep cleft that binds a metal ion along with a synergistic anion. In this work, the binding of vanadate as VO 2 + to the transferrins was studied by 51V quadrupolar central transition (QCT) NMR. Information about differences in the symmetry and motion of the bound metal ion was obtained from chemical shift and line width differences for serotransferrin (sTf), lactoferrin (lTf), and ovotransferrin (oTf). The effects of pH, ionic strength, and temperature on the 51V QCT NMR spectra of the bound VO 2 + cations showed that the N-lobe binding site of sTf is unique as compared to the other proteins. Properties of the quadrupolar central transition were also investigated, revealing that temperature, magnetic field strength, and NMR pulse angle all induce predictable changes on the second-order dynamic frequency shift, spectral line width, and optimal pulse angle in the 51V NMR spectra. Analysis of NMR spectra of V(V) 2-oTf and V(V) 2-sTf at three magnetic fields allowed an estimation of the quadrupolar coupling constants for these binding sites. This indicates that the degree of coordination symmetry in the binding sites is as follows: sTf N < sTf C < oTf N, C. Carbon-13 NMR studies revealed that VO 2 + binding, in contrast to di- and trivalent metal ions, has no requirement for a synergistic anion.

Synthesis, characterization and crystal structure of cyclic vanadate complexes with monosaccharide derivatives having a free adjacent diol system

A new approach to the study of reactions between vanadate and monosaccharide derivatives by introducing them into an acetonitrile medium has been elaborated. Based on this approach, a crystalline product of the reaction of [NBun4][H2VO4] with methyl O-4,6-benzylidene-α-D-mannopyranoside (H2L1) has been obtained, [NBun4]2[(VO2L1)2], and its structure has been determined by X-ray crystallography. The anion comprises a dinuclear V2(µ-O)2 centre and two deprotonated H2L1 molecules. Each vanadium atom is bound to the deprotonated vicinal cis-diol of one mannopyranoside ring resulting in a five-membered ring cyclic complex. The geometry of the two five-co-ordinated vanadium(V) atoms is intermediate between a square pyramid and a trigonal bipyramid. A complex with a similar formula [NBun4]2[(VO2L3)2]{H2L3= 5′-O-[(p-methoxyphenyl)diphenylmethyl]uridine}, has also been prepared and spectroscopically characterized. Multinuclear NMR studies and conductivity measurements in acetonitrile provided strong evidence that the dimeric structure of both complexes is maintained in solution. Vanadium-51 NMR titration studies in acetonitrile solutions showed that the chelation ability follows the order L3 > L1 > L2(H2L2= methyl O-4,6-benzylidene-α-D-glucopyranoside). Molecular modelling suggested that the O–⋯ O– distance and dihedral angle between the adjacent hydroxyl groups in a sugar ring are the determining factors for vanadium chelation.

Oxidation of alkylaromatic compounds with hydrogen peroxide catalyzed by mixed addenda Keggin heteropolyanions

Keggin type mixed addenda heteropolyanions containing vanadium atoms such as PV 2Mo 10O 5− 40 are shown to be effective catalysts for the oxidation of alkylaromatic compounds to the respective acetates or alcohols and aldehydes or ketones using 30% hydrogen peroxide as oxidant. Use of spectroscopic techniques including UV-Vis, IR, vanadium-51 and phosphorus-31 NMR, and ESR shows that the H 5PV 2Mo 10O 40 compound is not degraded during the catalytic cycle. Oxidation proceeds by homolytic cleavage of H 5PV 2Mo 10O 40-peroxo intermediates. The resulting hydroperoxy and hydroxy radicals initiate the formation of benzyl radicals which lead to the product formation.

Bonding states of surface vanadium(V) oxide phases on silica: structural characterization by vanadium-51 NMR and Raman spectroscopy

The coordination and local order of vanadium(V) surface oxides on silica are examined by 51 V spin echo and MAS NMR, as well as by Raman spectroscopy. Comparison with corresponding data on two crystallographically characterized model compounds, [Ph 3 SiO] 3 VO and [(c-C 6 H 11 ) 7 (Si 7 O 12 )VO] 2 , reveals unambiguously that the vanadia species found at the silica surface is a three-legged (SiO) 3 V=O unit. These results support the hypothesis that silsesquioxanes are appropriate model systems for hydroxylated silica surfaces

Characterization of vanadium oxide catalysts supported on titania-zirconia by solid-state vanadium-51 and proton NMR spectroscopy

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCharacterization of vanadium oxide catalysts supported on titania-zirconia by solid-state vanadium-51 and proton NMR spectroscopyB. Mahipal Reddy, E. Padmanabha Reddy, S. T. Srinivas, V. M. Mastikhin, A. V. Nosov, and O. B. LapinaCite this: J. Phys. Chem. 1992, 96, 17, 7076–7078Publication Date (Print):August 1, 1992Publication History Published online1 May 2002Published inissue 1 August 1992https://doi.org/10.1021/j100196a043RIGHTS & PERMISSIONSArticle Views186Altmetric-Citations28LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (381 KB) Get e-Alerts

1H and 51V NMR studies of the interaction of vanadate and 2-vanadio-3-phosphoglycerate with phosphoglycerate mutase.

The formation of complexes of vanadate with 2-phosphoglycerate and 3-phosphoglycerate have been studied using 51V nuclear magnetic resonance spectroscopy. Signals attributed to two 2,3-diphosphoglycerate analogues, 2-vanadio-3-phosphoglycerate and 2-phospho-3-vanadioglycerate, were detected but were not fully resolved from signals of inorganic vanadate and the anhydride formed between vanadate and the phosphate ester moieties of the individual phosphoglycerates. Equilibrium constants for formation of the two 2,3-bisphosphate analogues were estimated as 2.5 M-1 for 2-vanadio-3-phosphoglycerate and 0.2 M-1 for 2-phospho-3-vanadioglycerate. The results of the binding study are fully consistent with non-cooperativity in the binding of vanadiophosphoglycerate to the two active sites of phosphoglycerate mutase (PGM). 2-Vanadio-3-phosphoglycerate was found to bind to the dephospho form of phosphoglycerate mutase with a dissociation constant of about 1 x 10(-11) M at pH 7 and 7 x 10(-11) M at pH 8. Three signals attributed to histidine residues were observed in the 1H NMR spectrum of phosphoglycerate mutase. Two of these signals and also an additional signal, tentatively attributed to a tryptophan, underwent a chemical shift change when the vanadiophosphoglycerate complex was bound to the enzyme. The results obtained here are in accord with these vanadate-phosphoglycerate complexes being much more potent inhibitors of phosphoglycerate mutase than either monomeric or dimeric vanadate. The dissociation constant of 10(-11) M for 2-vanadio-3-phosphoglycerate is about 4 orders of magnitude smaller than the Km for PGM, a result in accordance with the vanadiophosphoglycerates being transition state analogues for the phosphorylation of PGM by 2,3-diphosphoglycerate.(ABSTRACT TRUNCATED AT 250 WORDS)

Vanadate interactions with bovine copper,zinc-superoxide dismutase as probed by vanadium-51 NMR spectroscopy

Vanadate interactions with bovine copper,zinc-superoxide dismutase as probed by vanadium-51 NMR spectroscopy

Proton and vanadium-51 NMR investigation of the complexes formed between vanadate and nucleosides

Proton and vanadium-51 NMR investigation of the complexes formed between vanadate and nucleosides

Vanadium-51 NMR study of vanadate binding to myosin and its subfragment 1

The binding of various forms of vanadate to myosin and myosin subfragment 1 (S-1) was studied by 51V NMR at increasing vanadate concentrations between 0.06 and 1.0 mM. The distribution of the various forms of vanadate in the solution depended on the total concentration of vanadate. At low concentrations, the predominant vanadate form was monomeric, while at high concentration, it was tetrameric. The presence of myosin or S-1 in the solution produced a significant broadening of the signal of each form of vanadate, indicating that all of them bind to the protein. Addition of ATP, which does not affect the 51V NMR spectra in the absence of proteins, causes their significant alteration in the presence of myosin or S-1. The changes, which include the broadening of the signal of the monomeric and the narrowing of the signal of the oligomeric vanadate forms, indicate that more monomeric and less oligomeric vanadate binds to the proteins in the presence than in the absence of ATP. Irradiation by near-UV light in the presence of vanadate cleaves S-1 at three specific sites--at 23, 31, and 74 kDa from the N-terminus. The cleavages at 23 and 31 kDa are specifically inhibited by the addition of ATP. The vanadate-associated photocleavage of S-1 also depends on the total concentration of vanadate; it is observed only when the concentration of vanadate is at least 0.2 mM. This was also the lowest concentration at which oligomeric vanadate was detected in the 51V NMR spectra. From the parallel concentration dependence of the photocleavage and the appearance of the tetrameric vanadate, it is concluded that photocleavage occurs only when tetrameric vanadate binds to S-1.

Characterization of vanadium oxide catalysts supported on tin dioxide by vanadium-51 and proton solid-state NMR spectroscopy

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCharacterization of vanadium oxide catalysts supported on tin dioxide by vanadium-51 and proton solid-state NMR spectroscopyK. Narsimha, B. Mahipal. Reddy, P. Kanta. Rao, and V. M. MastikhinCite this: J. Phys. Chem. 1990, 94, 19, 7336–7337Publication Date (Print):September 1, 1990Publication History Published online1 May 2002Published inissue 1 September 1990https://doi.org/10.1021/j100382a003RIGHTS & PERMISSIONSArticle Views91Altmetric-Citations17LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (260 KB) Get e-Alerts

Solid-state vanadium-51 NMR structural studies on supported vanadium(V) oxide catalysts: vanadium oxide surface layers on alumina and titania supports

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSolid-state vanadium-51 NMR structural studies on supported vanadium(V) oxide catalysts: vanadium oxide surface layers on alumina and titania supportsHellmut Eckert and Israel E. WachsCite this: J. Phys. Chem. 1989, 93, 18, 6796–6805Publication Date (Print):September 1, 1989Publication History Published online1 May 2002Published inissue 1 September 1989https://doi.org/10.1021/j100355a043RIGHTS & PERMISSIONSArticle Views1300Altmetric-Citations328LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts

Vanadium-51 NMR investigation of the interactions of vanadate with hydroxypyridines and pyridinecarboxylates in aqueous solution

The condensation of vanadate with salicylate, with pyridine, and with a variety of hydroxypyridines and pyridinecarboxylates in aqueous solution has been studied by using {sup 51}V nuclear magnetic resonance spectroscopy. Vanadium atom, ligand, and hydrogen ion concentration studies have been carried out. Compared with the other ligands, pyridine and 3-hydroxypyridine undergo comparatively weak interactions with vanadate. 2-Hydroxybenzoate (salicylate) and 2-hydroxy-3-pyridinecarboxylate (2-hydroxynicotinate) react only weakly as chelating ligands to give products that appear to have octahedral symmetry. No evidence for condensation of vanadate between the hydroxyl and the nitrogen of 2-hydroxynicotinate was obtained. 2-Pyridinecarboxylate (picolinate) proved to be a good chelating agent to form a mixture of mono- and bis(ligand) species of apparent octahedral coordination. A further mono(ligand) product that was tentatively assigned a pentacoordinate coordination was also formed. 3-Hydroxy-3-pyridinecarboxylate (3-hydroxypicolinate) formed a complex mixture of products, with condensation of vanadate between the nitrogen and carboxylate and possibly between the carboxylate and the hydroxyl group occurring. pH studies allowed the proton stoichiometry for the various condensations to be obtained. Formation constants for the various condensation products from specified reactants have been obtained and are reported in this study. 32 refs., 8 figs., 1 tab.

Vanadium-51 NMR as a probe of vanadium(V) coorination to human apotransferrin

Vanadium-51 NMR as a probe of vanadium(V) coorination to human apotransferrin

Investigation of silica-supported vanadium oxide catalysts: preparation and characterization by vanadium-51 NMR and x-ray photoelectron spectroscopy

Characterization by /sup 51/V NMR of the vanadium species adsorbed on silica-supported catalysts, prepared by impregnation of silica by solutions of ammonium vanadate at various pH values, has been followed from the initial step (impregnating solutions and wet samples) to the final step of preparation (calcined solids in dry air). At first, by use of the classical high-resolution NMR, the major species both in the impregnating solutions and on the wet solids have been identified for the different initial pH, and relative quantitative evaluations have been performed. Preparations at pH 11 give a major proportion of tetrahedra V/sub 4/O/sub 12//sup 4 -/ species, while at pH 4 vanadium oxide precipitates on silica. Second, the observations by solid-state NMR of these dried samples have shown that an important content of tetrahedral species was deposited on the solids prepared with the pH 11 initial solution (with a vanadium loading corresponding to the monolayer coverage limit, as determined further by XPS for the calcined series of samples), while only octahedral vanadium entities are detected for lower pH values. These species exhibit only few distortions; thus no support effect was evidenced in these dried samples. However, after further dehydration of the samples by calcinationmore » in dry air, the tetrahedral species (pH 11 samples) are much more affected than the octahedral entities, due probably to the formation of V-O-Si bonds, and this observation could be in correlation with the existence of the monolayer coverage limit observed only with these samples. The rehydration treatment breaks these bonds and restores a NMR signal of tetrahedral species.« less